Technical Field
The present invention relates to transistor devices, and more particularly to carbon nanotube transistors with protected metal contacts.
Description of the Related Art
Among all the candidate materials for post-silicon era, carbon nanotubes (CNTs) have intrinsic ultra-thin body and exceptional electrical properties (high on current, superior current on/off ratio, long mean-free-path for ballistic transport, etc.), which makes them one of the most promising candidates for sub-10 nm technology node in semiconductor industry. The implementation of CNT-based complementary metal oxide semiconductor (CMOS) technology with low standby power dissipation requires both robust high-performance n-type field effect transistors (NFETs) and p-type field effect transistors (PFETs), which are usually realized by using low- and high-work function metal contacts to the intrinsic (undoped) CNT channel, respectively.
While CNT p-type metal contacts (typically Pd) have been extensively studied and proven to be air-stable and robust, n-type metal contacts (typically Sc and Er) are usually prone to react with oxygen and hence suffer from severe degradation over time through oxidation in air. This oxidation problem leads to low-yield and unstable NFETs in device fabrication. To avoid the oxidation of CNT n-type metal contact, another layer of metal (typically Au) is usually deposited on top to prevent the oxidation from the top surface. However, oxidation from the sidewalls could still dramatically degrade the contact properties.